JPS60243335A - Air-fuel ratio controlling apparatus - Google Patents

Abstract

PURPOSE:To prevent rough idling operation of an engine, by increasing the fuel supply rate when the engine speed becomes lower than a tolerable value, and thereby raising the engine speed promptly even in case that variation of the combustion pressure is increased abruptly at the time of idling operation of the engine. CONSTITUTION:A pulse generator 2 connected to a crankshaft of an engine 1 generates pulse signals at equal intervals of the stroke volume and the crank angle, and a detector 3 gives an output signal to an amplifier 4 through detection of the above pulse signals. Further, pressure sensors 5, provided one for each cylinder of the engine, detect pressure in respective combustion chambers and furnish the pressure signals to the amplifier 4, which in turn gives output signals to an arithmetic means 6 by amplifying and scaling the above pressure signals. The arithmetic means 6 calculates the mean effective pressure, the variation value of the mean effective pressure and the engine speed of each cylinder at each cycle of the engine, and a control means 7 gives control signals to fuel injection valves 8 provided one for each cylinder. Thus, aimed objects and required effects of this invention can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device that changes the amount of fuel supplied in accordance with the magnitude of fluctuations in combustion pressure. It is.

Conventional Technology As an air-fuel ratio control device that can minimize the air-fuel ratio while suppressing torque fluctuations to an allowable value, the present applicant has already proposed a pressure sensor for detecting the pressure inside the combustion chamber in Japanese Patent Application No. 59-5694. I suggested what I used. That is, the fuel supply amount is controlled so that the fluctuation in combustion pressure falls within an allowable value. However, according to this air-fuel ratio control device, if the engine speed drops too much, even if the fuel is controlled to be increased due to large fluctuations in combustion pressure, it takes a certain amount of time before the fuel is actually increased. During this period, there is a risk of rough idling and, in some cases, engine stalling.

Problems to be Solved by the Invention An object of the present invention is to allow the engine speed to rise quickly even when fluctuations in combustion pressure suddenly increase, especially during idling operation, thereby preventing the risk of rough idling or engine stalling. With the goal.

Means for Solving the Problems In order to solve the above problems, the present invention provides a pressure sensor for detecting combustion pressure, a means for detecting engine speed, a fuel supply means for supplying fuel to the engine, and a combustion pressure sensor. control means for changing the amount of fuel supplied by the fuel supply means according to the magnitude of fluctuation in the amount of fuel supplied, the control means increasing the amount of fuel supplied when the engine speed becomes lower than the allowable rotation speed. An air-fuel ratio control device is provided.

Operation The air-fuel ratio control device according to the present invention increases the amount of fuel supplied when the fluctuation in combustion pressure is larger than a set value. Further, when the fluctuation in fuel pressure is smaller than the set value, if the engine speed is larger than the allowable value, the amount of fuel supplied is decreased, and if the engine speed is smaller than the allowable value, the amount of fuel supplied is increased.

Example The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 shows an example in which the present invention is applied to a four-cylinder engine,
The engine body 1 is provided with a pulse generator 2 connected to a crankshaft, and a detector 3 is provided near the pulse generator 2. A pulse generator 2 generates a pulse signal every equal stroke volume of the engine and every equal crank angle, and a detector 3 detects this pulse signal and outputs it to an amplifier 4.

Further, a pressure sensor 5 is attached to the engine body 1 in correspondence with each cylinder. These pressure sensors 5 are built into the spark plug of each cylinder or are separate from the spark plug, and detect the pressure inside the combustion chamber and output the pressure signal to the amplifier 4.

The amplifier 4 shapes the waveforms of the pulse signal and the pressure signal, amplifies them, scales them, and outputs the scaled signals to the arithmetic unit 6. From the input signal, the calculator 6 calculates the indicated average effective pressure (Pi) for each cylinder for each cycle, the average value of this Pl (lower i), and the fluctuation value of Pi (ΔPi=l).
Pi-Pil) and engine rotational speed (N), and outputs the calculation results to the control means 7. The control means 7 determines the amount of fuel supplied to each cylinder based on the signal input from the calculator 6, as will be described later, and outputs a control signal to the fuel injection valve 8 provided for each cylinder. The fuel injection valve 8 opens based on a control signal from the control means 7 to perform fuel injection.

Note that although it is preferable that the arithmetic unit 6 and the control means 7 are constituted by a microcomputer, they may be constituted by other arithmetic circuits.

The control means 7 calculates the fuel injection amount according to the flowchart shown in FIG. 5, and for this calculation,
The maximum permissible fluctuation value ΔPimaχ of Pi and the minimum idle rotation speed Nidmin are stored.

ΔPimax corresponds to the limit of engine roughness.

The fluctuation value ΔPi of Pl changes as shown in FIG. 2 with respect to the air-fuel ratio A/F, and in this diagram, the portion indicated by the broken line B indicates a state in which misfire may occur.

However, even in the solid line, in the part C where the air-fuel ratio is high, the combustion pressure fluctuates too much and the vehicle vibrates greatly.
Passengers feel uncomfortable. However, the permissible limit ΔPimax
This value is stored in the control means 7.

N idmin indicates a limit value below which engine stall will occur if the engine speed drops further. Of the engine speeds, the idle speed Nid in particular changes with respect to the air-fuel ratio A/F as shown in Figure 3, but the D portion is the portion that causes engine stalling, so Nid must be set higher than this. Must be. However, in reality, simply preventing the engine from stalling is insufficient; when the water temperature is low, it is necessary to increase the engine speed somewhat to warm it up. Therefore, N idmin is equal to the water temperature TII as shown in Figure 4.
It is preferable to change it with respect to H.

The control means 7 determines the injection amount of the fuel injection valve 8 for each cylinder based on the above data. FIG. 5 shows the procedure of processing executed by the control means 7 in each cycle.

In step 11, input is received from a conventionally known engine controller (not shown). Based on the signal indicating that the throttle valve is fully closed and the signal indicating that the transmission is in the neutral state, it is determined whether or not the vehicle is currently idling. If the vehicle is not idling, the process ends, and if the vehicle is idling, steps 12 and subsequent steps are executed. In step 12,
The ΔPi of each cylinder calculated in the calculator 6 is read, and this ΔPi is set to ΔP imax in step 13.
compared to The fact that ΔPi is larger than ΔP imax indicates that the fluctuation value of the combustion pressure exceeds the permissible value, and the process moves to step 14 to enrich the air-fuel ratio (where τ is the injection amount τ). ) is α
will be increased only. This α is, for example, 4% of the current injection amount.
It is. In step 13, ΔPi becomes ΔPimax
If it is determined that the combustion pressure is below, this indicates that the fluctuation value of the combustion pressure is within the permissible range, and then step 15 is executed. Step 15 determines whether Nid is greater than Nidmin. If Nid is larger than Nidmin, the current rotational speed is high enough to prevent engine stalling, and the process then proceeds to step 16, where the fuel injection amount τ is reduced by β in order to thin the air-fuel ratio. This β is
For example, it is 2% of the current injection amount. If it is determined in step 15 that Nid is less than or equal to N idmin,
Since the current rotational speed is likely to cause rough idling or engine stalling, the process moves to step 14, where the fuel injection amount is increased by α.

During idling operation, the fuel injection amount for each cylinder, that is, the air-fuel ratio, is controlled as described above, so engine vibration during idling operation is suppressed as much as possible, and drivability is improved. Furthermore, the idle speed can be lowered to a limit value, and fuel consumption during idle operation can be reduced. Furthermore, since the idle speed is prevented from falling below Nidmin, even if fluctuations in combustion pressure suddenly become large, the speed increases quickly, and rough idle or engine stalling is prevented.

Although the above embodiment applies the present invention to an engine having a fuel injection valve, the present invention can also be applied to an engine having a carburetor, and in this case, the air-fuel ratio can be adjusted by controlling the amount of air bleed. Just control it.

Effects of the Invention As described above, according to the present invention, it is possible to prevent the operation of the engine from becoming unstable during idling operation, and to prevent the engine from becoming unstable during idle operation. can be increased to prevent rough idling and engine stalling.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the relationship between combustion pressure and air-fuel ratio, Fig. 3 is a graph showing the relationship between idle speed and air-fuel ratio, and Fig. 4 is a graph showing the relationship between idle speed and air-fuel ratio. A graph showing the relationship between the minimum idle speed and water temperature, and FIG. 5 is a flowchart showing the control by the control means. 5... Pressure sensor, 7... Control means, 8... Fuel injection valve (fuel supply means). Patent applicant Toyota Motor Corporation Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Takashi Matsuura Patent attorney Akira Yamaguchi Patent attorney Masaya Nishiyama Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A pressure sensor for detecting combustion pressure, a means for detecting engine speed, a fuel supply means for supplying fuel to the engine, and a fuel supply amount of the fuel supply means according to the magnitude of fluctuation in combustion pressure. 1. An air-fuel ratio control device comprising: control means for increasing the fuel supply amount when the engine speed becomes lower than an allowable speed.